KR20190133131A - Nonaqueous electrolyte solution, nonaqueous electrolyte secondary battery, and method of producing nonaqueous electrolyte secondary battery - Google Patents

Abstract

The present invention relates to a nonaqueous electrolyte solution used in a nonaqueous electrolyte secondary battery, which contains, as a nonaqueous solvent, cyclic carbonate and fluorinated carboxylic acid ester having two fluorine atoms on an alpha-carbon atom derived from carboxylic acid.

Description

Nonaqueous Electrolyte, Non-aqueous Electrolyte Secondary Battery and Non-Aqueous Electrolyte Secondary Battery Manufacturing Method

The present invention relates to a method for producing a nonaqueous electrolyte, a nonaqueous electrolyte secondary battery and a nonaqueous electrolyte secondary battery.

A lithium ion secondary battery or other nonaqueous electrolyte secondary battery has a small size, a light weight, a high energy density, and an excellent output density as compared with a conventional battery. For this reason, in recent years, it is used suitably as a vehicle power supply for hybrid cars, electric vehicles, etc. Generally, it is preferable that the electrolyte solution used for this kind of nonaqueous electrolyte secondary battery has a property which is hard to receive oxidation. In other words, an electrolyte having a wide potential window is preferable.

As electrolyte solution used for a nonaqueous electrolyte secondary battery, what melt | dissolved supporting salts, such as lithium salt, in carbonate solvents, such as ethylene carbonate, a propylene carbonate, and diethyl carbonate, is used. On the other hand, from the viewpoint of further performance improvement, such as high energy density of a secondary battery, the electrolyte solution using the solvent which is harder to oxidize than such a carbonate solvent is desired. As a solvent which is harder to oxidize than a carbonate type solvent, using a fluorinated solvent is examined. A fluorinated solvent is a solvent in which a fluorine atom is introduced into a molecule. As a technical document regarding an electrolytic solution using a fluorinated solvent, Japanese Patent Application Laid-Open No. 2016-027548 is mentioned.

Japanese Unexamined Patent Application Publication No. 2016-027548 proposes to use a mixed solvent of methyl fluoride propionate and fluorinated cyclic carbonate as a nonaqueous solvent of a nonaqueous electrolyte in a nonaqueous electrolyte secondary battery having a positive electrode, a negative electrode, and a nonaqueous electrolyte. . The same document describes that such a configuration makes it possible to suppress side reactions during charge storage. However, according to the investigation by the present inventors, the fluorinated solvent which introduce | transduced the fluorine atom in a solvent molecule tends to increase a viscosity, and there exists a fault that the electrical conductivity of a nonaqueous electrolyte is easy to fall. There is a demand for a nonaqueous electrolyte that can achieve high electrical conductivity while improving oxidation resistance of the nonaqueous electrolyte.

The present invention is to provide a nonaqueous electrolyte which is excellent in oxidation resistance and can realize high electrical conductivity. Moreover, another object is to provide the nonaqueous electrolyte secondary battery provided with such a nonaqueous electrolyte solution, and the manufacturing method of this nonaqueous electrolyte secondary battery.

The present inventors searched for the fluorinated solvent which can implement | achieve a high electrical conductivity by containing in a nonaqueous electrolyte solution. As a result, it was found out that high conductivity can be achieved by using a combination of a fluorinated carboxylic acid ester having a specific fluorination rate and a fluorinated position with a cyclic carbonate relative to the ester skeleton, thereby completing the present invention.

The 1st aspect of this invention relates to the nonaqueous electrolyte solution used for a nonaqueous electrolyte secondary battery. This non-aqueous electrolyte is a non-aqueous solvent and includes a fluorinated carboxylic acid ester (XCF ₂ COOR) and a cyclic carbonate having two fluorine atoms on the α carbon atom (the first carbon atom adjacent to COOR) derived from carboxylic acid. It includes. Thus, by using the fluorinated carboxylic acid ester which has two fluorine atoms, and cyclic carbonate in combination on the alpha carbon atom derived from carboxylic acid in carboxylic acid ester, the oxidation resistance and conductivity of a nonaqueous electrolyte solution are improved significantly. You can.

In the first aspect of the present invention, the ratio of the content of the fluorinated carboxylic acid ester and the cyclic carbonate (fluorinated carboxylic acid ester: cyclic carbonate) is 50:50 to 95: 5 based on volume. Range may be sufficient. If it exists in the range of ratio of content of such fluorinated carboxylic acid ester and cyclic carbonate, the electroconductive improvement effect of a nonaqueous electrolyte solution can be exhibited more suitably.

The 1st aspect of this invention may also contain the 1st compound (compound A) represented by the following general formula (A) as said fluorinated carboxylic acid ester. By containing such a 1st compound, the electroconductivity of a nonaqueous electrolyte solution can be improved more.

-R ₁ in the first compound is -CH ₃ , -CH ₂ CH ₃ , -CF ₂ H, -CFH ₂ , -CF ₃ , -CH ₂ CF ₃ , -CH ₂ CF ₂ H, -CH ₂ CFH ₂ , -CFHCF ₃ , -CFHCF ₂ H, -CFHCFH ₂ , -CF ₂ CF ₃ , -CF ₂ CF ₂ H and -CF ₂ CFH ₂ . -X may be selected from the group consisting of -H, -CF ₂ H, -CFH _2, and -CH ₃ .

The 1st aspect of this invention may also contain the 2nd compound (compound B) represented by the following general formula (B) as said cyclic carbonate. By containing such a 2nd compound, the electroconductivity of a nonaqueous electrolyte solution can be improved more.

Wherein R ₂ and R ₃ in the second compound are the same or different substituents, and R ₂ and R ₃ in the second compound are each independently a group consisting of an alkyl group having a hydrogen atom, a fluorine atom, an alkyl group and a fluorine atom; It may be selected from.

The first aspect of the present invention may further include, as an additive, a third compound (compound C) represented by the following general formula (C) and a fourth compound (compound D) represented by the following general formula (D). do. By combining such a third compound and a fourth compound in a nonaqueous electrolyte, the cycle durability of a secondary battery constructed using the nonaqueous electrolyte can be greatly improved.

Here, R <_4> in a 3rd compound may be a C2-C8 alkylene group or the C2-C8 alkylene group which has a substituent.

Here, R <_5> and R <_6> in a 4th compound may respectively independently be selected from the group which consists of a hydrogen atom, a fluorine atom, an alkyl group, the alkyl group which has a fluorine atom, and an aryl group. Alternatively, R ₅ and R ₆ may be an aromatic ring or an aliphatic ring which is bonded to each other.

The first aspect of the present invention further provides, as the fluorinated carboxylic acid ester, CHF ₂ COOCH ₃ , CH ₃ CF ₂ COOCH ₃ , CFH ₂ CF ₂ COOCH ₃ , CF ₂ HCF ₂ COOCH ₃ , CHF ₂ COOC ₂ H ₅ , CH ₃ CF ₂ COOC ₂ H ₅ , CFH ₂ CF ₂ COOC ₂ H ₅ , CF ₂ HCF ₂ COOC ₂ H ₅ , CHF ₂ COOCH ₃ may be included.

The first aspect of the present invention may further include CHF ₂ COOCH ₃ as the fluorinated carboxylic acid ester.

According to a first aspect of the present invention, the cyclic carbonate includes ethylene carbonate, monofluoroethylene carbonate, propylene carbonate, ethyl ethylene carbonate, (fluoromethyl) ethylene carbonate, ( Trifluoromethyl) ethylene carbonate and 1,2-difluoroethylene carbonate may further be included.

In the first aspect of the present invention, the third compound may be succinic anhydride, and the fourth compound may be maleic anhydride.

The first aspect of the present invention may further include any of lithium difluorooxalatoborate and lithium bis (oxalato) borate as the additive.

The 2nd aspect of this invention relates to the nonaqueous electrolyte secondary battery provided with a positive electrode, a negative electrode, and a nonaqueous electrolyte. The nonaqueous electrolyte solution which this nonaqueous electrolyte secondary battery is equipped with as a nonaqueous solvent contains cyclic carbonate and fluorinated carboxylic acid ester which has two fluorine atoms on the alpha carbon atom derived from carboxylic acid. The nonaqueous electrolyte secondary battery of such a structure has high electrical conductivity of a nonaqueous electrolyte, and can be a high performance thing.

According to a second aspect of the present invention, the ratio of the content of the fluorinated carboxylic acid ester and the cyclic carbonate (fluorinated carboxylic acid ester: cyclic carbonate) is 50:50 to 95: 5 based on volume. Range may be sufficient. If it exists in the range of the ratio of content of such fluorinated carboxylic acid ester and cyclic carbonate, a high performance secondary battery with low initial stage resistance can be implement | achieved, for example.

The second aspect of the present invention may further contain the first compound as the fluorinated carboxylic acid ester. By containing such a first compound in the nonaqueous electrolyte, a higher performance secondary battery can be realized.

The second aspect of the present invention may further include the second compound as the cyclic carbonate. By containing such a compound B in a nonaqueous electrolyte, a high performance secondary battery with low initial resistance can be realized, for example.

The third aspect of the present invention relates to a method for producing a nonaqueous electrolyte secondary battery. This manufacturing method includes the process of building a battery assembly. The battery assembly is constructed by accommodating a positive electrode and a negative electrode in a battery case together with a nonaqueous electrolyte, and the nonaqueous electrolyte contained in the battery assembly includes a nonaqueous solvent and an additive. As said non-aqueous solvent, cyclic carbonate and fluorinated carboxylic acid ester which has two fluorine atoms on the alpha carbon atom derived from carboxylic acid are included. The said additive contains the said 3rd compound and the said 4th compound. It also includes an initial charging step of performing an initial charging process on the battery assembly. According to the above-described manufacturing method, for example, a high performance secondary battery having low initial resistance and excellent cycle durability can be manufactured.

The technical and industrial significance, features, and advantages of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings. Like numbers refer to like elements in the figures.
1 is a diagram schematically showing a lithium ion secondary battery according to one embodiment.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described, referring drawings suitably. In addition, the dimensional relationship (length, width, thickness, etc.) in each figure does not reflect actual dimensional relationship. In addition, the structure and manufacturing method of the electrode body provided with the positive electrode and the negative electrode which are matters other than what is specifically mentioned in this specification, and are necessary for the implementation of this invention, the structure and manufacturing method of a separator, the shape of a battery (case), etc. And general techniques related to battery construction can be understood as design matters of those skilled in the art based on the prior art in the art. The present invention can be practiced based on the contents disclosed herein and common technical knowledge in the field.

In addition, in this specification, a nonaqueous electrolyte secondary battery means the secondary battery provided with a nonaqueous electrolyte. The nonaqueous electrolyte is typically an electrolyte containing a supporting salt (supported electrolyte) in the nonaqueous solvent. In addition, a lithium ion secondary battery means the secondary battery which charges / discharges by the movement of lithium ion between stationary electrodes using lithium ion as electrolyte ion. In addition, an electrode active material means the material which can reversibly occlude and discharge | release the chemical species used as a charge carrier. A charge carrier is lithium ion in a lithium ion secondary battery. In addition, below, although the nonaqueous electrolyte solution used for a lithium ion secondary battery is demonstrated, it does not intend to limit the application target of this invention.

<Non-aqueous electrolyte solution>

The nonaqueous electrolyte solution which concerns on the preferable one aspect of the technique disclosed here is a nonaqueous electrolyte solution used for a lithium ion secondary battery, and typically shows a liquid state at normal temperature, such as 25 degreeC, Preferably it is -20 degreeC-60 degreeC, etc. The liquid phase is always indicated within the temperature range of use. As the nonaqueous electrolyte, a solution in which the supporting salt is dissolved or dispersed in the nonaqueous solvent can be suitably employed. As a supporting salt, it is a lithium salt in a lithium ion secondary battery, for example, The thing similar to a general lithium ion secondary battery can be selected suitably, and can be employ | adopted. For example, lithium salts such as LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , Li (CF ₃ SO ₂ ) ₂ N, LiN (FSO ₂ ) ₂ , LiCF ₃ SO _3, and the like can be used. Especially, LiPF ₆ can be employ | adopted suitably. It is preferable to prepare the density | concentration of the said support salt so that it may exist in the range of 0.5 mol / L-3.0 mol / L, and 0.5 mol / L-2.0 mol / L are more preferable.

<Fluorinated carboxylic acid ester>

The nonaqueous electrolyte solution disclosed here contains the fluorinated carboxylic acid ester and cyclic carbonate which have two fluorine atoms on the alpha carbon atom derived from carboxylic acid as a nonaqueous solvent. The fluorinated carboxylic acid ester is a compound represented by XCF ₂ COOR as a general formula, and _{two of} hydrogen atoms (H) directly bonded to α carbon atoms derived from carboxylic acid are substituted with fluorine atoms (F). Thus, by using the combination of fluorinated methyl acetate and cyclic carbonate which have two fluorine atoms on the specific carbon atom in carboxylic acid ester, oxidation resistance and electrical conductivity of a nonaqueous electrolyte solution can be improved significantly. The reason why such an effect is obtained is not particularly limited, but can be considered as follows, for example. That is, cyclic carbonates are liable to dissociate the supporting salts in the electrolyte into cations and anions by coordinating cations such as lithium to the cyclic carbonates, while fluorinated carboxylic acid esters having fluorine atoms in order to increase oxidation resistance and the like. When used in combination with, the viscosity of the electrolyte is likely to increase. Therefore, viscosity increase is more excellent than the dissociation property of electrolyte solution, and electrical conductivity may become a tendency for a fall. On the contrary, the fluorinated carboxylic acid ester having two fluorine atoms on the α carbon atom derived from carboxylic acid has high compatibility with cyclic carbonate and good diffusibility, and is combined with cyclic carbonate. The viscosity increase hardly occurs even if used. It is thought that this contributes to the improvement of the electrical conductivity.

The fluorinated carboxylic acid ester is not particularly limited as long as it has two fluorine atoms on the α carbon atom derived from carboxylic acid. For example, the total number of carbon atoms in the fluorinated carboxylic acid ester is typically 3 to 15, and from the viewpoint of suppressing the viscosity increase, preferably 3 to 10, more preferably 3 to 8, More preferably, it is 3-5. The number of fluorine atoms in the fluorinated carboxylic acid ester is not particularly limited as long as it is two or more in one molecule from the viewpoint of improving oxidation resistance and the like, but is typically 2 to 20, preferably 2 to 20 15, More preferably, it is 2-8, More preferably, it is 2-5. In the fluorinated carboxylic acid ester, fluorinated carboxylic acid ester in which one or two or more hydrogen atoms bonded to the carbon atoms constituting the main chain are further substituted with substituents other than fluorine atoms may be used independently. As a suitable example of the said fluorinated carboxylic acid ester, the compound A represented by the following general formula (A) is mentioned.

Here, -R ₁ in Compound A is -CH ₃ , -CH ₂ CH ₃ , -CF ₂ H, -CFH ₂ , -CF ₃ , -CH ₂ CF ₃ , -CH ₂ CF ₂ H, -CH ₂ CFH ₂ , -CFHCF ₃ , -CFHCF ₂ H, -CFHCFH ₂ , -CF ₂ CF ₃ , -CF ₂ CF ₂ H and -CF ₂ CFH ₂ . -X is selected from the group consisting of -H (hydrogen atom), -CF ₂ H, -CFH ₂ and -CH ₃ . Among them, CHF ₂ COOCH ₃ , CH ₃ CF ₂ COOCH ₃ , CFH ₂ CF ₂ COOCH ₃ , CF ₂ HCF ₂ COOCH ₃ , CHF ₂ COOC ₂ H ₅ , CH ₃ CF ₂ COOC ₂ H ₅ , CFH ₂ CF ₂ COOC ₂ H ₅ , CF ₂ HCF ₂ COOC ₂ H ₅ is preferable, in particular, R ₁ is CH ₃ , and X is a hydrogen atom, CHF ₂ COOCH ₃ ( Methyl difluoroacetate: MDFA) is preferred.

The ratio (volume basis) of the content of the fluorinated carboxylic acid ester and the cyclic carbonate is not particularly limited. From the viewpoint of better exhibiting the effect of using fluorinated carboxylic acid ester and cyclic carbonate in combination, the volume ratio (fluorinated carboxylic acid ester: cyclic carbonate) of fluorinated carboxylic acid ester and cyclic carbonate is 50. It is suitable that it is: 50-95: 5, It is preferable that it is 60: 40-95: 5, It is more preferable that it is 70: 30-95: 5. It is effective to make content of a fluorinated carboxylic acid ester more than content of cyclic carbonate from a viewpoint of obtaining high electrical conductivity. The technique disclosed herein can be preferably carried out, for example, in a form in which the volume ratio of the fluorinated carboxylic acid ester and the cyclic carbonate is 80:20 to 90:10.

<Cyclic carbonate>

As cyclic carbonate used together with the said fluorinated carboxylic acid ester, various cyclic carbonates known to be usable as a nonaqueous solvent in the nonaqueous electrolyte of a lithium ion secondary battery can be used without particular limitation. For example, ethylene carbonate (EC; C ₃ H ₄ O ₃ : ethylene carbonate or 1,3-dioxolan-2-one), propylene carbonate (PC), butylene carbonate (BC), Pentylene carbonate, vinylene carbonate (VC), or derivatives thereof are mentioned suitably. Especially, it is preferable to use EC and its derivative which show high dielectric constant. As a suitable example of EC and its derivative (s), the compound B represented by following General formula (B) is mentioned.

Here, R <_2> and R <_3> in the compound B are the same or different substituents, and are each independently selected from the group which consists of an alkyl group which may be substituted by the hydrogen atom, a fluorine atom, and a fluorine atom. That is, in a preferable embodiment, even if one or two of the four hydrogen atoms (H) directly bonded to the carbon atoms constituting the heterocycle (5-membered ring) of EC are substituted with a fluorine atom or a fluorine atom in the ethylene carbonate derivative It is substituted by the alkyl group to become. In addition, in this specification, an ethylene carbonate derivative is a concept containing each geometric isomer. In addition, the substituted positions of R <_2> , R <_3> of an ethylene carbonate derivative are respectively independently 1 position or 2 positions.

In the said compound B, at least one of the two substituents R <_2> and R <_3> on the carbon atom which comprises a heterocycle, for example, both may be the alkyl group which may be substituted by the fluorine atom. R <_2> and R <_3> may be linear or branched form. From the standpoint of lowering the viscosity of the nonaqueous electrolyte, improving the conductivity, and the like, a compound B having 1 to 12 carbon atoms in total of R ₂ and R ₃ can be preferably employed. It is also possible to employ Compound B in which the total carbon atoms of R ₂ and R ₃ are 1 to 6, typically 1 to 4, for example 1 or 2. When there are too many carbon atoms, the viscosity of a nonaqueous electrolyte solution may become high, or ion conductivity may fall. For the same reason, it is usually preferable that the alkyl group is linear. For example, R ₂ and R ₃ may be an alkyl group having 1 to 6 carbon atoms. In addition, R ₂ and R ₃ may be 1 to 4, typically 1 or 2, alkyl groups. Examples of the alkyl group having 1 to 6 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, t-butyl group, n-pentyl group, 1-methylbutyl group, 2-methylbutyl group, 3-methylbutyl group, 1-methyl-2-methylpropyl group, 2,2-dimethylpropyl group, hexyl group, etc. are illustrated. In addition, from the viewpoint of increasing the oxidation resistance, a group having a structure in which one or two or more hydrogen atoms of these alkyl chain skeletons are substituted with fluorine atoms, that is, a fluorinated alkyl group having 1 to 6 carbon atoms may be used. It is preferable that the hydrogen atom couple | bonded with the carbon atom of the terminal in an alkyl chain skeleton is a fluorinated alkyl group substituted with the fluorine atom. In the case of employing a fluorinated alkyl group, the number of fluorine atoms is not particularly limited as long as it is at least one in the alkyl chain skeleton, but is preferably 1 to 12, preferably 1 to 7, for example, 1 to 5, typically 1 to 3 You may make it.

As one suitable example of compound B, one of R ₂ and R ₃ is a hydrogen atom, the other is a fluorine atom, one of R ₂ and R ₃ is a hydrogen atom, and the other is an alkyl group having 4 or less carbon atoms Examples of the phosphorus structure, one of R ₂ and R ₃ are hydrogen atoms, the other is a fluorinated alkyl group having 4 or less carbon atoms, a structure in which both R ₂ and R ₃ are hydrogen atoms, and the like. As an embodiment of such compound B, ethylene carbonate (EC), monofluoroethylene carbonate (MFEC), propylene carbonate (PC), ethyl ethylene carbonate, (fluoromethyl) ethylene carbonate (FPC), (difluoromethyl) ethylene carbonate (DFPC), (trifluoromethyl) ethylene carbonate (TFPC), etc. are mentioned. Especially, EC, MFEC, PC, FPC, and TFPC are preferable from the viewpoint of appropriately expressing the action such as the improvement of conductivity by Compound B.

As one suitable example of compound B, one of R ₂ and R ₃ is a fluorine atom, the other is an alkyl group having 4 or less carbon atoms, one of R ₂ and R ₃ is a fluorine atom, and the other is a carbon atom The structure etc. which are several fluorinated alkyl groups, the structure whose both R <_2> and R <_3> are a fluorine atom, etc. are illustrated. As an embodiment of such compound B, 1,2-difluoroethylene carbonate (DFEC), 1-fluoro-2-methylethylene carbonate, 1-fluoro-2-ethylethylene carbonate, 1 -Fluoro-2- (fluoromethyl) ethylenecarbonate, 1-fluoro-2- (difluoromethyl) ethylenecarbonate, 1-fluoro-2- (trifluoromethyl) ethylenecarbonate Nate etc. are mentioned. Especially, DFEC is preferable from a viewpoint which expresses effects, such as the improvement of electroconductivity by compound B, suitably.

As another example of the compound B, one of R ₂ and R ₃ is an alkyl group having 4 or less carbon atoms, and the other is a fluorinated alkyl group having 4 or less carbon atoms, and both of R ₂ and R ₃ have 4 carbon atoms The structure etc. which are the following alkyl groups, the structure whose both R <_2> and R <_3> are fluorinated alkyl groups of 4 or less carbon atoms are illustrated. As a specific example of such a compound B, 1,2-dimethylethylene carbonate, 1,2-diethylethylene carbonate, 1-fluoromethyl-2-methylethylene carbonate, 1-difluoromethyl- 2-methylethylene carbonate, 1-trifluoromethyl-2-methylethylene carbonate, 1-fluoromethyl-2- (fluoromethyl) ethylene carbonate, 1-difluoromethyl-2- (Fluoromethyl) ethylene carbonate, etc. are mentioned.

The nonaqueous electrolyte solution disclosed here may contain individually 1 type of cyclic carbonate mentioned above, and may contain it in combination of 2 or more type. By combining with such a cyclic carbonate and the said fluorinated carboxylic acid ester in a nonaqueous electrolyte solution, the nonaqueous electrolyte solution which has high electrical conductivity, and also the high performance nonaqueous electrolyte secondary battery while suppressing the oxidative decomposition of the nonaqueous electrolyte solution in a positive electrode It can be realized.

The nonaqueous electrolyte solution disclosed here may further contain the compound C represented by the following general formula (C) and the compound D represented by the following general formula (D) as an additive. By combining the compound C which is such a saturated cyclic carboxylic anhydride and the compound D which is an unsaturated cyclic carboxylic anhydride, in a nonaqueous electrolyte solution, the cycle durability of the secondary battery constructed using this nonaqueous electrolyte solution can be improved significantly.

<Saturated cyclic carboxylic anhydride (Compound C)>

R ₄ constituting the heterocycle in the compound C is an alkylene group having 2 to 8 carbon atoms which may have a substituent.

In the compound C, the alkylene group may be linear or branched. For example, the number of carbon atoms of R ₄ from 2 to 6, for example 2 to 4, and typically may be preferably employed a two or three compounds C. Examples of the linear alkylene group having 2 to 8 carbon atoms include ethylene group, trimethylene group, tetramethylene group, pentamethylene group, hexamethylene group, heptamethylene group, and the like. As the branched alkylene group, a propylene group, Isopyrene group, isobutylene group, 2-methyl trimethylene group, isohexylene group, etc. are mentioned. The alkylene group may be substituted with one or a plurality of hydrogen atoms with substituents such as halogen group, nitro group, isocyanate group, cyanate group, ester group, ketone group, alkyl ether group and cyano group. However, two or less are preferable in one molecule, and, as for the number of the said other substituents, one or less in one molecule is more preferable.

As one suitable example of compound C, succinic anhydride (SA), glutaric anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, 1,2-cyclohexanedicarboxylic anhydride, 4-cyclohexene-1,2-dicarboxylic acid anhydride, 5-norbornene-2,3-dicarboxylic acid anhydride, 3-methyl-4-cyclohexene-1,2-dicarboxylic acid anhydride, Phenyl succinic anhydride, 2-phenyl glutaric anhydride, 2,2-dimethyl succinic anhydride, allyl succinic anhydride, monofluorosuccinic anhydride, trifluoromethyl succinic anhydride, tetrafluorosuccinic anhydride and the like. Among them, from the viewpoint of suitably expressing the action of improving the cycle durability by compound C, R ₄ is an ethylene group (-CH ₂ CH ₂ -) is a succinic anhydride are preferred.

The nonaqueous electrolyte solution disclosed here may contain individually 1 type of compound C which is the saturated cyclic carboxylic anhydride mentioned above, and may contain it in combination of 2 or more type.

Unsaturated cyclic carboxylic anhydride (Compound D)

R ₅ and R ₆ in the compound D are each independently selected from the group consisting of an alkyl group or an aryl group which may be substituted with a hydrogen atom, a fluorine atom and a fluorine atom. Alternatively, R ₅ and R ₆ may be bonded to each other to form an aromatic ring or an aliphatic ring.

In the compound D, at least one of, for example, both of the two substituents R ₅ and R ₆ on the carbon atom constituting the heterocycle may be an alkyl group or an aryl group. R <_5> and R <_6> may be linear or branched form. For example, the compound D whose total carbon atom number of R <_5> and R <_6> is 1-12 can be employ | adopted preferably. It is also possible to employ compounds D in which the total carbon atoms of R ₅ and R ₆ are 1 to 6, typically 1 to 4, for example 1 or 2. For example, R ₅ and R ₆ may be alkyl groups having 1 to 6 carbon atoms, for example 1 to 4, typically 1 or 2 carbon atoms. Examples of the alkyl group having 1 to 6 carbon atoms include methyl group, ethyl group, n-propyl group, isopropyl group, n-butyl group, isobutyl group, sec-butyl group, t-butyl group, n-pentyl group and 1-methyl A butyl group, 2-methylbutyl group, 3-methylbutyl group, 1-methyl-2-methylpropyl group, 2, 2- dimethylpropyl group, hexyl group, etc. are illustrated. Moreover, the group of the structure by which one or two or more hydrogen atoms of these alkyl chain skeletons were substituted by the fluorine atom, ie, the C1-C6 fluorinated alkyl group, may be sufficient. In the case of employing a fluorinated alkyl group, the number of fluorine atoms is not particularly limited as long as it is at least one in the alkyl chain skeleton, but is preferably 1 to 12, preferably 1 to 7, for example, 1 to 5, typically 1 to 3 You may make it.

As one suitable example of compound D, one of R ₅ and R ₆ is a hydrogen atom, the other is a fluorine atom: one of R ₅ and R ₆ is a hydrogen atom, and the other is an alkyl group having 4 or less carbon atoms Examples of the phosphorus structure, one of R ₅ and R ₆ are hydrogen atoms, the other is a fluorinated alkyl group having 4 or less carbon atoms, a structure in which both R ₅ and R ₆ are hydrogen atoms, and the like. As an embodiment of such a compound D, maleic anhydride (MA: maleic anhydride), methyl maleic anhydride (citraconic anhydride), 2,3-dimethylmaleic anhydride, ethyl maleic anhydride, fluoromethyl maleic anhydride , Trifluoromethyl maleic anhydride, fluoromaleic anhydride and the like. Among them, maleic anhydride is preferable from the viewpoint of suitably expressing the action such as improvement in cycle durability by the compound D.

As another example of the compound D, a structure in which one of R ₅ and R ₆ is a fluorine atom, the other is an alkyl group having 4 or less carbon atoms, one of R ₅ and R ₆ is a fluorine atom, and the other is a carbon atom number A structure of 4 or less fluorinated alkyl groups, a structure in which both R ₅ and R ₆ are fluorine atoms, one of R ₅ and R ₆ is an alkyl group having 4 or less carbon atoms, and the other is a fluorinated alkyl group having 4 or less carbon atoms structure, R ₅ and R ₆ are both an alkyl group in the number of 4 or less carbon atom structure, R is a fluorinated alkyl group of the structure or the like ₅ and R ₆ are both of the number of carbon atoms of 4 or less is illustrated in. As a specific example of such a compound D, difluoro maleic anhydride, 2-fluoro-3- methyl maleic anhydride, etc. are mentioned.

As another example of the compound D, a structure in which one of R ₅ and R ₆ is a hydrogen atom, the other is an aryl group, one of R ₅ and R ₆ is a fluorine atom, and the other is an aryl group, R ₅ and R ₆ One of these is an alkyl group which may be substituted with a fluorine atom, the other is a structure which is an aryl group, the structure whose both of R <_5> and R <_6> are an aryl group, etc. are illustrated. As a specific example of such a compound D, phenyl maleic anhydride, 2, 3- diphenyl maleic anhydride, etc. are mentioned.

In the compound D, two substituents R ₅ and R ₆ on the carbon atom constituting the heterocycle may be bonded to each other to form an aromatic ring or an aliphatic ring. As a specific example of such a compound D, 1-cyclohexene-1,2-dicarboxylic anhydride, 1-cyclopentene-1,2-dicarboxylic anhydride, phthalic anhydride, 1,2-naphthalic anhydride, tetra Fluorophthalic anhydride, and the like.

The nonaqueous electrolyte solution disclosed here may be included individually by 1 type of the compound D mentioned above, and may be included in combination of 2 or more type. By combining the compound D and the compound C described above in the nonaqueous electrolyte, the cycle durability of the secondary battery constructed using the nonaqueous electrolyte can be greatly improved. The reason why such an effect is obtained is not particularly limited, but is considered as follows, for example. That is, since the non-aqueous electrolyte solution containing the fluorinated carboxylic acid ester and the cyclic carbonate has excellent ion conductivity and tends to be reduced in resistance, the decomposition reaction of the non-aqueous electrolyte solution occurs at the negative electrode during charge and discharge. In some cases, cycle durability may be lowered. On the contrary, in the nonaqueous electrolyte solution containing the compound C and the compound D, a high-quality film containing a component derived from the compound C and the compound D is formed on the negative electrode surface at the time of initial charge. By such a coating, the decomposition reaction at the negative electrode can be suppressed. It is thought that this contributes to the improvement of cycle durability.

It is suitable that content of the said compound C shall be 0.005 mass% or more with respect to the total mass of the said nonaqueous electrolyte, for example. Content of the said compound C is from a viewpoint of cycle durability improvement etc., Preferably it is 0.01 mass% or more, More preferably, it is 0.05 mass% or more, More preferably, it is 0.1 mass% or more, Especially preferably, it is 0.5 mass% or more. . Although the upper limit of content of the said compound C is not specifically limited, From a viewpoint of solubility, etc., it is usually suitable to be 10 mass% or less normally, Preferably it is 5 mass% or less, More preferably, it is 3 mass% or less, More preferably, it is Preferably it is 2 mass% or less. The technique disclosed here can be preferably implemented in the form of content of the said compound C, for example 0.005 mass% or more and 10 mass% or less, typically 0.5 mass% or more and 2 mass% or less.

It is suitable that content of the said compound D shall be 0.005 mass% or more with respect to the total mass of the said nonaqueous electrolyte, for example. Content of the said compound D is from a viewpoint of cycle durability improvement etc., Preferably it is 0.01 mass% or more, More preferably, it is 0.05 mass% or more, More preferably, it is 0.1 mass% or more, Especially preferably, it is 0.5 mass% or more. . Although the upper limit of content of the said compound D is not specifically limited, Usually, from a viewpoint of solubility, etc., it is suitable to usually be 10 mass% or less, Preferably it is 5 mass% or less, More preferably, it is 3 mass% or less, More preferably, it is Preferably it is 2 mass% or less, Especially preferably, it is 1 mass% or less. The technique disclosed here can be preferably implemented in a form in which the content of the compound D is, for example, 0.005% by mass or more and 10% by mass or less, typically 0.5% by mass or more and 2% by mass or less.

Although the mixing ratio of the compound C and the compound D in the nonaqueous electrolytic solution is not particularly limited, the ratio (compound D / compound C) of the content of the compound D to the compound C is preferably about 5 or less, preferably Is 4 or less, More preferably, it is 3.5 or less, More preferably, it is 3 or less, Especially preferably, it is 2 or less. Moreover, it is suitable to make the said content ratio into about 0.1 or more, Preferably it is 0.2 or more, More preferably, it is 0.3 or more, More preferably, it is 0.4 or more, Especially preferably, it is 0.5 or more.

The nonaqueous electrolyte solution disclosed here may contain film forming agents (third film forming agents) other than the compound C and the compound D. Examples of such third film formers include lithium difluorooxalatoborate (LiDFOB), lithium bis (oxalato) borate (LiBOB), vinylene carbonate (VC), monofluoroethylene carbonate (MFEC) and 1, 3- propane sultone (PS) are mentioned. Especially, LiDFOB and LiBOB are preferable. It is suitable that the quantity of the said 3rd film forming agent is 50 mass% or less, for example, 1 mass%-50 mass% in the total mass of the film forming agent contained in a nonaqueous electrolyte, Preferably it is 35 mass % Or less, for example, 10 mass%-35 mass%.

As described above, the nonaqueous electrolyte disclosed herein can be suitably used as a component of various types of lithium ion secondary batteries in view of excellent oxidation resistance and high conductivity as described above. Except for using the fluorinated carboxylic acid ester and cyclic carbonate disclosed here as a non-aqueous solvent of electrolyte solution, the process similar to a conventional can be employ | adopted and a lithium ion secondary battery can be constructed. Although it is not intended to be specifically limited, although the lithium ion secondary battery shown typically in FIG. 1 is demonstrated as an example as a schematic structure of the secondary battery provided with the nonaqueous electrolyte solution which concerns on this embodiment, the application target of this invention is described. It is not intended to be limiting.

In the lithium ion secondary battery 100 shown in FIG. 1, the wound electrode body 80 of the form in which the positive electrode sheet 10 and the negative electrode sheet 20 are wound flat through the separator sheet 40 is not shown. Together with the nonaqueous electrolyte solution, the battery case 50 is housed in a flat box-shaped battery case 50.

The battery case 50 includes a flat rectangular parallelepiped (box-shaped) battery case body 52 with an open top, and a lid 54 covering the opening. As a material of the battery case 50, a relatively light metal such as aluminum or an aluminum alloy can be preferably used. The upper surface (cover 54) of the battery case 50 is electrically connected to the negative electrode of the positive electrode terminal 70 and the wound electrode body 80 for external connection, which are electrically connected to the positive electrode of the wound electrode body 80. The negative electrode terminal 72 is provided. The lid 54 is further provided with a safety valve 55 for discharging gas generated inside the battery case 50 to the outside of the case 50, similarly to a battery case of a conventional lithium ion secondary battery.

Inside the battery case 50, a flat wound electrode body 80 is housed together with the nonaqueous electrolyte (not shown) described above. The wound electrode body 80 includes a long sheet positive electrode (positive electrode sheet) 10 and a long sheet negative electrode (negative electrode sheet) 20.

<Positive electrode>

The positive electrode sheet 10 includes an elongated positive electrode current collector, and a positive electrode active material layer 14 formed along at least one surface thereof, typically on both sides thereof, along a long direction. Such a positive electrode sheet 10 can be produced by, for example, applying a composition formed by dispersing a forming component of the positive electrode active material layer in a suitable solvent such as N-methyl-2-pyrrolidone to the surface of the positive electrode current collector and drying it. have. The formation component of the said positive electrode active material layer can contain a positive electrode active material, a electrically conductive material used as needed, a binder (binder), etc. Moreover, as a positive electrode electrical power collector, the electroconductive member containing the metal with favorable electroconductivity, such as aluminum, nickel, titanium, stainless steel, can be employ | adopted suitably.

As for the positive electrode of the lithium ion secondary battery disclosed here, the upper limit operating potential in the range of 0%-100% of SOC (state of charge) is 4.3V or more, Preferably it is 4.35V or more, More preferably, based on metal lithium. Is 4.6 V, more preferably 4.9 V or more. In general, the highest operating potential is between SOC 0% and 100% when the SOC is 100%. Therefore, the upper limit of the operating potential of the positive electrode is normally determined through the operating potential of the positive electrode in SOC 100%, that is, a full charge state. I can figure it out. In addition, in the technique disclosed herein, the operating upper limit potential of the positive electrode in the range of 0% to 100% of SOC is typically 4.3 V or more and 5.5 V or less, for example, 4.9 V or more and 5.2 V or less, based on metal lithium. It can be preferably applied to a lithium ion secondary battery.

The positive electrode showing such an operation upper limit potential can be suitably realized by using a positive electrode active material having a maximum value of the operating potential in the range of 0% to 100% SOC of 4.3 V (vs. Li / Li ⁺ ) or more. Especially, the operating potential in SOC 100% exceeds 4.3V on a metallic lithium basis, Preferably it is 4.5V or more, More preferably, it is 4.6V or more, Furthermore, use of the positive electrode active material of 4.9V or more is preferable. By using the positive electrode active material having the above operating potential, higher energy density can be realized. Moreover, also in such a high potential positive electrode, side reaction with a positive electrode can be suppressed suitably by using the said difluoro acetate and cyclic carbonate for a nonaqueous electrolyte solution.

Here, the operating potential of a positive electrode active material can be measured as follows, for example. That is, first, the positive electrode containing the positive electrode active material as a measurement object is used as the working electrode WE, such a working electrode, metal lithium as the counter electrode CE and the reference electrode RE, and a non-aqueous electrolyte solution. Build it. Next, the SOC of this cell is adjusted at 5% intervals from 0 to 100% based on the theoretical capacity of the cell. Such SOC can be adjusted by, for example, constant current charging between WE-CE using a general charging / discharging device, a potentiometer, or the like. After leaving the cell adjusted to each SOC state for 1 hour, the potential between WE-RE is measured to set the potential to the operating potential (vs. Li / Li ⁺ ) of the positive electrode active material in the SOC state.

As an example of the positive electrode active material which can realize such a high potential suitably, the lithium manganese complex oxide of a spinel structure is mentioned. Among them, as a preferable embodiment, a lithium nickel manganese composite oxide having a spinel structure containing Li, Ni, and Mn as constituent metal elements can be mentioned. More specifically, the general formula (I) below: a lithium-nickel-manganese composite oxide of a spinel structure represented by _{Li x (Ni y Mn 2-} yz Me 1 z) O 4 + α (I) can be given. Here, Me ¹ may be any transition metal element or typical metal element other than Ni, Mn, for example, is one or two or more selected from Fe, Ti, Co, Cu, Cr, Zn and Al. . Alternatively, one or two or more semimetal elements or nonmetal elements selected from B, Si, and Ge may be used. Further, x is 0.8 ≦ x ≦ 1.2, y is 0 <y, z is 0 ≦ z, y + z <2, typically y + z ≦ 1; α is -0.2 ≦ α ≦ 0.2 and is a value determined to satisfy the charge neutral condition. In a preferable embodiment, y is 0.2 ≦ y ≦ 1.0, more preferably 0.4 ≦ y ≦ 0.6, for example 0.45 ≦ y ≦ 0.55; z is 0≤z <1.0, for example, 0≤z≤0.3. LiNi _0.5 Mn _1.5 O ₄ etc. are mentioned as an example of the lithium nickel manganese complex oxide represented by the said general formula. The spinel structure lithium nickel manganese composite oxide may contribute to the high energy density of the battery. In addition, whether or not a compound (oxide) has a spinel structure can be determined, for example, by X-ray structural analysis, preferably by single crystal X-ray structural analysis. Specifically, it can discriminate by X-ray diffraction measurement using CuKα ray.

As another example of the positive electrode active materials disclosed herein, represented by the general formula LiMe _² O ^2, and typically it includes lithium-transition metal composite oxide of a layered structure. Here, Me ² contains at least 1 type of transition metal elements, such as Ni, Co, Mn, and can further contain other metal elements or nonmetal elements. Such a layered lithium transition metal composite oxide may contribute to high capacity of the battery.

As another example of the positive electrode active material disclosed here, lithium transition metal compounds, such as phosphate of an olivine type structure represented by general formula: LiMe ³ PO ₄ ; Here, Me ³ contains at least 1 sort (s) of transition metal elements, such as Mn, Fe, Co, and can further contain another metal element or a nonmetal element. Specific examples include LiMnPO ₄ , LiFePO ₄ , LiCoPO ₄ , and the like.

Other examples of the positive electrode active material disclosed herein include a solid solution of LiMe ² O ₂ and Li ₂ Me ⁴ O ₃ . Here, LiMe ² O ₂ represents a composition represented by the general formula described above. In addition, Me ⁴ of Li ₂ Me ⁴ O ₃ may include at least one of transition metal elements such as Mn, Fe, Co, and containing other metal elements or non-metallic element further. Specific examples include Li ₂ MnO ₃ and the like. As a specific example of the said solid solution, the solid solution represented by 0.5LiNi _1/3 Co _1/3 Mn _1/3 O ₂ -0.5Li ₂ MnO ₃ can be mentioned.

The positive electrode active material mentioned above can be used individually by 1 type or in combination of 2 or more types. Especially, a positive electrode active material is 50 mass% or more, typically 50-100 mass%, for example 70 in all the positive electrode active materials using the lithium nickel manganese complex oxide of the spinel structure represented by the said General formula (I). It is preferable to contain in a ratio of 100-100 mass%, Preferably it is 80-100 mass%, and the positive electrode active material which consists only of lithium nickel manganese complex oxide of a spinel structure is more preferable.

In the technique disclosed herein, the positive electrode active material is preferably in the form of particles having an average particle diameter of 1 μm to 20 μm, typically 2 μm to 15 μm. In addition, in this specification, unless an average particle diameter is specifically limited, in the particle size distribution of the volume reference based on a laser diffraction light scattering method, it is the particle size equivalent to 50 volume% of cumulative frequencies from the particle side of small particle size ( D ₅₀ : median diameter).

<Other positive electrode active material layer components>

The positive electrode active material layer may contain additives such as a conductive material and a binder (binder) in addition to the positive electrode active material. As the conductive material, conductive powder materials such as carbon powder and carbon fiber are preferably used. As carbon powder, various carbon black (CB), for example, acetylene black (AB) is preferable.

Various polymer materials are mentioned as a binder. For example, when a dispersion medium forms the positive electrode active material layer using the water-based composition which is water or the mixed solvent which has water as a main component, a water-soluble or water-dispersible polymer material can be used. Examples of the water-soluble or water-dispersible polymer material include cellulose polymers such as carboxymethyl cellulose (CMC), fluorine resins such as polytetrafluoroethylene (PTFE), and rubbers such as styrene butadiene rubber (SBR). Or when forming a positive electrode active material layer using the solvent type composition whose dispersion medium is an organic solvent mainly, vinyl halide resins, such as polyvinylidene fluoride (PVdF), polyalkylene oxides, such as polyethylene oxide (PEO), etc. Polymeric materials can be used. Such a binder can be used individually by 1 type or in combination of 2 or more types. The polymer material exemplified above may be used as a thickener, dispersant or other additives in addition to being used as a binder.

The proportion of the positive electrode active material in the entire positive electrode active material layer is approximately 50% by mass or more, and typically 50% by mass to 97% by mass is appropriate, and usually 70% by mass to 95% by mass, for example, 75% by mass to It is preferable that it is 95 mass%. In addition, when using a electrically conductive material, the ratio of the electrically conductive material to the whole positive electrode active material layer can be roughly 2 mass%-20 mass%, It is preferable to set it as roughly 2 mass%-15 mass% normally. In addition, when using a binder, the ratio of the binder which occupies for the whole positive electrode active material layer can be roughly 0.5 mass%-10 mass%, It is preferable to set it as roughly 1 mass%-5 mass% normally.

<Negative electrode>

The negative electrode sheet 20 includes an elongated negative electrode current collector and a negative electrode active material layer 24 formed along at least one surface thereof in the longitudinal direction. Such a negative electrode sheet 20 can be produced by, for example, applying a composition obtained by dispersing a forming component of the negative electrode active material layer in a suitable solvent such as water to the surface of the negative electrode current collector and drying it. The formation component of the said negative electrode active material layer can contain a negative electrode active material and the binder used as needed. As the negative electrode current collector, a conductive material containing a metal having good conductivity such as copper, nickel, titanium, or stainless steel can be suitably employed.

As the negative electrode active material, one kind or two or more kinds of substances conventionally used for lithium ion secondary batteries can be used without particular limitation. As an example of a negative electrode active material, a carbon material is mentioned, for example. Graphite carbon (graphite), amorphous carbon, etc. are mentioned as a representative example of a carbon material. A particulate carbon material (carbon particles) containing a graphite structure (layered structure) at least in part is preferably used. Especially, the use of the carbon material which has natural graphite as a main component is preferable. The natural graphite may be spherical graphite. Moreover, you may use the carbonaceous powder by which amorphous carbon was coated on the surface of graphite. In addition, as the negative electrode active material, metal oxide materials such as silicon oxide, titanium oxide, vanadium oxide, lithium titanium composite oxide (LTO), metal nitride materials such as lithium nitride, lithium cobalt composite nitride, and lithium nickel composite nitride It is also possible to use a single material such as a silicon material, a tin material, an alloy, a compound, or a composite material using the above material in combination. Among them, it is preferable to use a negative electrode active material having a reduction potential (vs. Li / Li ⁺ ) of about 0.5 V or less, for example, 0.2 V or less, typically 0.1 V or less. By using the negative electrode active material having the reduction potential, higher energy density can be realized. As a material which can become such a low potential, a natural graphite type carbon material is mentioned. In the technique disclosed herein, the negative electrode active material preferably has an average particle diameter of 10 µm to 30 µm, typically 15 µm to 25 µm.

<Other negative electrode active material layer structural components>

In addition to a negative electrode active material, a negative electrode active material layer can contain additives, such as a binder (binder) and a thickener, as needed. As a binder and a thickener used for a negative electrode active material layer, the thing similar to the binder demonstrated about the positive electrode active material layer can be used.

It is preferable that the ratio of the negative electrode active material which occupies for the whole negative electrode active material layer exceeds 50 mass% roughly, and is roughly 80-99.5 mass%, for example, 90-99 mass%. Moreover, it is preferable that the ratio of the binder which occupies for the whole negative electrode active material layer is roughly 0.5-5 mass%, for example, 1-2 mass%. Moreover, it is preferable that the ratio of the thickener which occupies for the whole negative electrode active material layer is roughly 0.5-5 mass%, for example, 1-2 mass%.

Between the positive electrode active material layer 14 and the negative electrode active material layer 24, two long sheet-like separators (separator sheet) 40 are arrange | positioned as an insulating layer which prevents direct contact of both. As the separator sheet 40, a porous sheet containing a resin such as polyethylene (PE), polypropylene (PP), polyester, cellulose, polyamide, a nonwoven fabric, or the like can be used.

The wound electrode body 80 is obtained by, for example, winding a laminate stacked in the order of the positive electrode sheet 10, the separator sheet 40, the negative electrode sheet 20, and the separator sheet 40 in the longitudinal direction. It can produce by shape | molding to a flat shape by pressing and winding up a winding object from a lateral direction.

In the width direction defined as the direction from the one end in the winding axial direction to the other end of the wound electrode body 80, the positive electrode active material layer 14 and the negative electrode formed on the surface of the positive electrode current collector at the center portion thereof. The negative electrode active material layer 24 formed on the surface of an electrical power collector is overlapped, and the winding core part laminated | stacked closely is formed. In addition, at both ends of the wound electrode body 80 in the winding axial direction, the positive electrode active material layer non-forming portion of the positive electrode sheet 10 and the negative electrode active material layer non-forming portion of the negative electrode sheet 20 are respectively pushed out from the wound core portion. have. And a positive electrode collector plate is provided in the positive electrode side push-out part, and a negative electrode collector plate is provided in the negative electrode side push-out part, respectively, and is electrically connected with the positive electrode terminal 70 and the negative electrode terminal 72, respectively.

<Method for producing lithium ion secondary battery>

The lithium ion secondary battery 100 having such a configuration may be manufactured through a battery assembly construction process and an initial charging process.

Battery Assembly Process

In the battery assembly construction step, the wound electrode body 80 including the positive electrode sheet 10 and the negative electrode sheet 20 is housed together with the nonaqueous electrolyte in a battery case to construct a battery assembly. Here, a battery assembly means the battery assembled to the form before performing an initial stage charging process in the battery manufacturing process. The battery assembly accommodates the wound electrode body 80 therein, for example, from the opening of the battery case 50, and installs the cover 54 in the opening of the case 50, and then attaches the cover 54 to the cover 54. The nonaqueous electrolyte can be injected from an injection hole (not shown) provided, and the injection hole can be sealed by welding or the like. In this embodiment, the nonaqueous electrolyte solution contained in a battery assembly contains the said fluorinated carboxylic acid ester and cyclic carbonate as a nonaqueous solvent. Moreover, the said nonaqueous electrolyte solution contains the said compound C and the said compound D as an additive.

Initial Charging Process

In the initial charging step, initial charging is performed on the battery assembly. Typically, an external power supply is connected between the positive electrode (positive electrode terminal) and the negative electrode (negative electrode terminal) of the battery assembly, and charged to a predetermined voltage range. Charging typically means constant current charging. Thereby, the high quality film | membrane containing the component derived from the said compound C and the said compound D is formed in the negative electrode surface.

What is necessary is just to set the voltage of initial stage charging so that the said compound C and the said compound D may electrically decompose, for example. As an example, when the negative electrode active material is a carbon material, the voltage between the negative electrode terminals may be charged until approximately 3V or more, typically 3.5V or more, for example, 4V to 5V. Such charging may be performed by the method of constant current charging (CC charging) from the start of charging until the battery voltage reaches a predetermined value, or by the method of constant voltage charging after reaching the predetermined voltage (CC-CV charging). You may do it. In addition, the charging rate at the time of constant current charge is 1C or less normally, Preferably you may be 0.1C-0.2C. According to the findings of the present inventors, the compound C and the compound D decompose relatively slowly when charged at a low rate of 1 C or less. And the film containing the compound of the said compound C and the said compound D is formed in the surface of a negative electrode so that it may be suppressed with sufficient compactness, for example, low resistance, and reactivity with a nonaqueous electrolyte solution sufficiently. Therefore, the effect of this structure can be exhibited at a higher level. In addition, although charging may be performed once, it can also be performed repeatedly twice or more, for example, interposing a discharge.

In this manner, the lithium ion secondary battery 100 according to the present embodiment can be manufactured.

Although the lithium ion secondary battery disclosed here can be used for various uses, it is characterized by the outstanding electroconductivity of a nonaqueous electrolyte solution. Therefore, utilizing these characteristics, it can use suitably for the use which requires high performance, such as low resistance. As such a use, the drive power supply mounted in vehicles, such as a plug-in hybrid vehicle, a hybrid vehicle, an electric vehicle, is mentioned, for example. Moreover, such a secondary battery can be used in the form of an assembled battery which typically consists of connecting several in series and / or in parallel.

Some embodiments of the present invention are described below, but the present invention is not intended to be limited to these embodiments.

(Test Example 1)

<Non-aqueous electrolyte solution>

Plural kinds of mixed solvents (non-aqueous solvent) having different compositions and volume ratios were prepared. LiPF ₆ as a supporting salt was mixed with these mixed solvents at a concentration of about 1 mol / liter to prepare the nonaqueous electrolyte solutions of Examples 1 to 22. About the nonaqueous electrolyte solution which concerns on each example, the composition and volume ratio of the used mixed solvent are put together in Table 1, and are shown. Here, to MDFA is, in Table 1 in the general formula _{(E), R 7 = CHF} 2, R 8 = difluoro corresponding to CH ₃ and ethyl-methyl, M ₂ FP is R ₇ = CHFCH _3, R ₈ Is a compound equivalent to = CH ₃ , M333TFP is a compound equivalent to R ₇ = CH ₂ CF ₃ , R ₈ = CH ₃ , M2333TFP is a compound equivalent to R ₇ = CHFCF ₃ , R ₈ = CH ₃ , and DMC Is a compound equivalent to R ₇ = OCH ₃ , R ₈ = CH ₃ , EMC is a compound equivalent to R ₇ = OCH ₃ , R ₈ = CH ₂ CH ₃ , and TFEMC is R ₇ = OCH ₃ , R ₈ = It is a compound corresponding to OCH ₂ CF ₃ , and DEC is a compound corresponding to R ₇ = OCH ₂ CH ₃ , R ₈ = CH ₂ CH ₃ . In addition, EC in Table 1 is a compound corresponded to R < ₂ > H, R < ₃ > H in the said General formula (B), PC is a compound corresponded to R < ₂ > CH <_3> , R < ₃ > H, MFEC is a compound equivalent to R ₂ = F, R ₃ = H, DFEC is a compound equivalent to R ₂ = F, R ₃ = F, and FPC is equivalent to R ₂ = CH ₂ F, R ₃ = H TFPC is a compound corresponding to R ₂ = CF ₃ and R ₃ = H.

<Measurement of conductivity>

Moreover, the electrical conductivity of the nonaqueous electrolyte of each case was measured. The conductivity measurement was measured at 25 ° C. using a conductivity meter Seven Multi manufactured by METTLER TOLEDO Corporation. The results are shown in the corresponding columns of Table 1.

As shown in Table 1, according to the nonaqueous electrolyte of Example 1 using MDFA (methyl difluoroacetate) and TFPC (cyclic carbonate), compared with Examples 2 to 4 using other fluorinated carboxylic acid esters and TFPC, The conductivity of the nonaqueous electrolyte solution could be improved. In this respect, it was confirmed that by using fluorinated carboxylic acid ester and TFPC having two fluorine atoms on the α carbon atom derived from carboxylic acid, high electrical conductivity improvement effect was realized while improving oxidation resistance. Moreover, when comparing Examples 6-13, even if there were too many ratios of MDFA, the electrical conductivity showed the tendency for at least to fall. In terms of electrical conductivity, the volume ratio of cyclic carbonate: MDFA is 50:50 to 5:95, preferably 30:70 to 10:90.

(Test Example 2)

In this example, a laminate cell (lithium ion secondary battery) was constructed using different nonaqueous electrolytes having various compositions and addition amounts of additives, and the performance thereof was evaluated.

Construction of Laminate Cell

The positive electrode of the laminated cell was produced as follows. First, a layered lithium nickel cobalt manganese composite oxide (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ) powder as a positive electrode active material, AB as a conductive material, PVdF as a binder, and a positive electrode active material: conductive material: binder Was mixed in NMP such that the mass ratio was 87: 10: 3 to prepare a composition for forming a positive electrode active material layer. The positive electrode in which the positive electrode active material layer was formed in the single side | surface of a positive electrode electrical power collector was produced by apply | coating this composition for positive electrode active material layer formation to the single side | surface of an elongate sheet-like aluminum foil (positive electrode collector).

The negative electrode of the laminated cell was produced as follows. First, the natural graphite as a negative electrode active material, SBR as a binder, and CMC as a thickener were dispersed in water so that the mass ratio of a negative electrode active material: binder: thickener may be 98: 1: 1, and the composition for negative electrode active material layers was prepared. The negative electrode in which the negative electrode active material layer was formed in the single side | surface of a negative electrode electrical power collector was produced by apply | coating this composition for negative electrode active material layers to the single side | surface of a long sheet-like copper foil (negative electrode collector).

As a separator of a laminate cell, the separator containing the base material of the microporous film (PP / PE / PP film) of the three-layered structure of polypropylene / polyethylene / polypropylene was prepared.

The laminate cell was constructed using the positive electrode, negative electrode, and separator prepared above. That is, the electrode body was produced by interposing a separator between the positive electrode and negative electrode produced above so that the active material layers of both electrodes may oppose. Subsequently, as a battery assembly building process, this electrode body was accommodated in the laminated bag-shaped battery container with a predetermined nonaqueous electrolyte solution, and the battery assembly was constructed.

The laminate cells of Examples 23 to 31 differ in the composition of the nonaqueous solvent in the nonaqueous electrolytic solution, the type of additives and the amount of addition. About the laminate cell which concerns on each example, the composition of the nonaqueous solvent used, the kind of additive, and addition amount are put together in Table 2, and are shown. Here, TFPC, MDFA, EC, DMC, EMC, M2FP, M333TFP, M2333TFP and TFEMC in Table 2 are as described above. SA in Table 2 is succinic anhydride corresponding to R ₄ = CH ₂ CH ₂ in General Formula (C), and MA is R ₅ = H, R ₆ = H in General Formula (D). It is equivalent to maleic anhydride.

As the initial charging step, the battery assembly is charged at a temperature of 25 ° C. until it reaches 4.3V at a constant current of 0.2C, and after reaching 4.3V, the current is briefly lowered to become a constant voltage at 4.3V. Charging was continued, and when electric current reached 0.02C, charging was complete | finished and it was set to the fully charged state, ie, SOC 100%. In this way, the laminate cells according to Examples 23 to 31 were constructed.

After the said initial charge, it discharged until it reached 3V by the constant current of 0.2C, and made the discharge capacity at this time an initial capacity. In addition, it adjusted to the state of SOC 34% at the temperature of 25 degreeC per lamination cell which concerns on each example. For each battery adjusted to 34% SOC, discharge was performed for 10 seconds at a rate of 30C, and the voltage drop during that time was measured. The internal resistance was computed by dividing the measured voltage drop by the electric current value at the time of discharge, and made it initial stage resistance. A result is shown in the column of the initial stage resistance ratio of Table 2. Here, it represents with the relative value when the initial resistance of Example 28 is set to 1.00.

<High temperature cycle test>

Each cell of Examples 23 to 31 was charged and discharged in a thermostatic chamber of about 50 ° C., charged until reaching 4.3 V at a constant current of 2 C, and then discharged until reaching 3 V at a constant current of 2 C. A high temperature cycle test was repeated 200 times in succession. The capacity retention rate was calculated from the initial capacity before the high temperature cycle test and the battery capacity after the high temperature cycle test. Here, the battery capacity after the high temperature cycle test was measured in the same procedure as the initial capacity described above. In addition, the said capacity retention ratio was calculated | required by (battery capacity after a high temperature cycling test / initial capacity before a high temperature cycling test) x100. The results are shown in the column of the capacity retention rate after 200 cycles in Table 2. In addition, the resistance increase rate was calculated from the initial resistance before the high temperature cycle test and the battery resistance after the high temperature cycle test. Here, the battery resistance after the high temperature cycle test was measured in the same procedure as the initial resistance described above. In addition, the said resistance increase rate was calculated | required by the initial resistance before battery resistance / high temperature cycling test after high temperature cycling test. The results are shown in the column of the resistance increase rate after 200 cycles in Table 2. Here, it represents with the relative value when the resistance increase rate of Example 28 is set to 1.00.

As shown in Table 2, the laminate cells of Examples 23 to 25 using a non-aqueous electrolyte in which MDFA (methyl difluoroacetate) and TFPC (cyclic carbonate) were used in combination and SA and MA were added were subjected to a high temperature cycle test. Even afterwards, a capacity retention rate of 80% or more could be achieved. Moreover, about the resistance increase rate, it became about the same as Example 28, and the favorable result was obtained.

(Test Example 3)

In this example, a spinel structure lithium nickel manganese composite oxide (LiNi _0.5 Mn _1.5 O ₄ ) powder is used instead of LiNi _1/3 Co _1/3 Mn _1/3 O ₂ as the positive electrode active material in Test Example 2, The laminated cells of Examples 32 to 36 were constructed in the same manner as in Test Example 2 except that the upper limit voltage was changed to 4.9 V and the lower limit voltage was 3.5 V in the charging step. In the same procedure as in Test Example 2, the initial resistance ratio, the capacity retention rate after 200 cycles, and the resistance increase rate after 200 cycles were measured. In this example, the upper limit voltage in the high temperature cycle test was set to 4.9V and the lower limit voltage to 3.5V. Table 3 shows the composition of the nonaqueous solvent used, the type of additives, the amount of addition, the initial resistance ratio, the capacity retention rate after 200 cycles, and the resistance increase rate after 200 cycles. In addition, the initial stage resistance ratio is shown by the relative value in the case where the initial stage resistance of Example 35 was set to 1.00 here. In addition, the resistance increase rate is shown by the relative value when the resistance increase rate of Example 35 is set to 1.00.

As shown in Table 3, in the laminate cell of Example 35 using the nonaqueous electrolyte containing EC, DMC, and EMC, the capacity retention rate after the high temperature cycle test was low because the nonaqueous electrolyte was oxidatively decomposed by use at a high potential. The battery resistance also tended to increase. On the other hand, the laminate cell of Example 32 which used MDFA and TFPC together, and used SA and MA addition nonaqueous electrolyte can achieve 80% or more of capacity | capacitance retention even after high-temperature cycle test, and is favorable also about resistance increase rate. Was obtained.

As mentioned above, although the specific example of this invention was described in detail, these are only illustrations and do not limit a claim. The invention disclosed herein may include various modifications and changes of the above-described specific examples.

Claims (13)

Non-aqueous electrolyte A non-aqueous electrolyte used for secondary batteries,
A non-aqueous solvent comprising a cyclic carbonate and a fluorinated carboxylic acid ester having two fluorine atoms on an α carbon atom derived from a carboxylic acid,
The volume ratio of the said fluorinated carboxylic acid ester: the said cyclic carbonate is 70: 30-95: 5, The nonaqueous electrolyte solution. The said fluorinated carboxylic acid ester contains the 1st compound represented by following General formula A,
-R ₁ in the first compound is -CH ₃ , -CH ₂ CH ₃ , -CF ₂ H, -CFH ₂ , -CF ₃ , -CH ₂ CF ₃ , -CH ₂ CF ₂ H, -CH ₂ CFH ₂ , -CFHCF ₃ , -CFHCF ₂ H, -CFHCFH ₂ , -CF ₂ CF ₃ , -CF ₂ CF ₂ H and -CF ₂ CFH ₂ , wherein -X in the first compound is- A nonaqueous electrolyte solution selected from the group consisting of H, -CF ₂ H, -CFH _2, and -CH ₃ .

The said cyclic carbonate contains the 2nd compound represented by following General formula B, The said cyclic carbonate is a
R ₂ and R ₃ in the second compound are the same or different substituents, and R ₂ and R ₃ in the second compound are each independently selected from the group consisting of a hydrogen atom, a fluorine atom, an alkyl group and an alkyl group having a fluorine atom Chosen, non-aqueous electrolyte.

The method of claim 1 or 2, further comprising an additive contained in the non-aqueous solvent, wherein the additive includes a third compound represented by the following general formula (C) and a fourth compound represented by the following general formula (D). and,
R ₄ of the third compound is an alkylene group having 2 to 8 carbon atoms or an alkylene group having 2 to 8 carbon atoms having a substituent, and R ₅ and R ₆ in the fourth compound are each independently, A nonaqueous electrolyte solution selected from the group consisting of a hydrogen atom, a fluorine atom, an alkyl group, an alkyl group having a fluorine atom and an aryl group, or R ₅ and R ₆ are bonded to each other to form an aromatic ring or an aliphatic ring.

According to claim 2, The fluorinated carboxylic acid ester is, CHF ₂ COOCH ₃ , CH ₃ CF ₂ COOCH ₃ , CFH ₂ CF ₂ COOCH ₃ , CF ₂ HCF ₂ COOCH ₃ , CHF ₂ COOC ₂ H ₅ , CH ₃ CF ₂ COOC ₂ H ₅ , CFH ₂ CF ₂ COOC ₂ H ₅ , CF ₂ HCF ₂ COA ₂ H ₅ A non-aqueous electrolyte. The method of claim 5, wherein the non-aqueous electrolytic solution of the fluorinated carboxylic acid esters, including CHF ₂ COOCH _3. The cyclic carbonate is ethylene carbonate, monofluoroethylene carbonate, propylene carbonate, ethyl ethylene carbonate, (fluoromethyl) ethylene carbonate, (trifluoro Non-aqueous electrolyte solution containing any of romethyl) ethylene carbonate and 1,2-difluoroethylene carbonate. The nonaqueous electrolyte solution of Claim 4 whose said 3rd compound is succinic anhydride and the said 4th compound is maleic anhydride. The nonaqueous electrolyte solution of Claim 4 in which the said additive contains any of lithium difluoro oxalatoborate and lithium bis (oxalato) borate. In a nonaqueous electrolyte secondary battery comprising a positive electrode, a negative electrode and a nonaqueous electrolyte,
A nonaqueous solvent contained in the nonaqueous electrolyte, the nonaqueous solvent includes a cyclic carbonate and a fluorinated carboxylic acid ester having two fluorine atoms on an α carbon atom derived from a carboxylic acid,
The non-aqueous electrolyte secondary battery of said fluorinated carboxylic acid ester: the volume ratio of the said cyclic carbonate is 70: 30-95: 5. The said fluorinated carboxylic acid ester contains the 1st compound represented by following General formula A,
-R ₁ in the first compound is -CH ₃ , -CH ₂ CH ₃ , -CF ₂ H, -CFH ₂ , -CF ₃ , -CH ₂ CF ₃ , -CH ₂ CF ₂ H, -CH ₂ CFH ₂ , -CFHCF ₃ , -CFHCF ₂ H, -CFHCFH ₂ , -CF ₂ CF ₃ , -CF ₂ CF ₂ H and -CF ₂ CFH ₂ , wherein -X in the first compound is- A nonaqueous electrolyte secondary battery selected from the group consisting of H, -CF ₂ H, -CFH _2, and -CH ₃ .

The said cyclic carbonate contains the 2nd compound represented by following General formula B,
R ₂ and R ₃ in the second compound are the same or different substituents, and R ₂ and R ₃ in the second compound are each independently selected from the group consisting of an alkyl group having a hydrogen atom, a fluorine atom, an alkyl group and a fluorine atom Nonaqueous electrolyte secondary battery selected.

In the manufacturing method of a nonaqueous electrolyte secondary battery,
Constructing a battery assembly, and performing an initial charging process on said battery assembly,
The battery assembly is constructed by accommodating a positive electrode and a negative electrode together with a nonaqueous electrolyte in a battery case, wherein the nonaqueous electrolyte contained in the battery assembly includes a nonaqueous solvent and an additive, and the nonaqueous solvent includes cyclic carbonate and And a fluorinated carboxylic acid ester having two fluorine atoms on an α carbon atom derived from a carboxylic acid, wherein the additive is a third compound represented by the following general formula (C) and a fourth compound represented by the following general formula (D). Compound,
The volume ratio of the said fluorinated carboxylic acid ester: the said cyclic carbonate is 70: 30-95: 5,
R <_4> in a said 3rd compound is a C2-C8 alkylene group which has a C2-C8 alkylene group or a substituent,
R ₅ and R ₆ in the fourth compound are each independently any of a hydrogen atom, a fluorine atom, an alkyl group, an alkyl group having a fluorine atom and an aryl group, or an aromatic ring or aliphatic having R ₅ and R ₆ bonded to each other; The manufacturing method of the nonaqueous electrolyte secondary battery which forms the ring.

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